Hypophysial and meningeal melanocytes in the Zucker rat

Melanocytes in regenerative medicine applications and disease modeling

Melanocytes are dendritic cells localized in skin, eyes, hair follicles, ears, heart and central nervous system. They are characterized by the presence of melanosomes enriched in melanin which are responsible for skin, eye and hair pigmentation. They also have different functions in photoprotection, immunity and sound perception. Melanocyte dysfunction can cause pigmentary disorders, hearing and vision impairments or increased cancer susceptibility. This review focuses on the role of melanocytes in homeostasis and disease, before discussing their potential in regenerative medicine applications, such as for disease modeling, drug testing or therapy development using stem cell technologies, tissue engineering and extracellular vesicles.

Pericyte Ontogeny: The Use of Chimeras to Track a Cell Lineage of Diverse Germ Line Origins

The goal of lineage tracing is to understand body formation over time by discovering which cells are the progeny of a specific, identified, ancestral progenitor. Subsidiary questions include unequivocal identification of what they have become, how many descendants develop, whether they live or die, and where they are located in the tissue or body at the end of the window examined. A classical approach in experimental embryology, lineage tracing continues to be used in developmental biology and stem cell and cancer research, wherever cellular potential and behavior need to be studied in multiple dimensions, of which one is time. Each technical approach has its advantages and drawbacks. This chapter, with some previously unpublished data, will concentrate nonexclusively on the use of interspecies chimeras to explore the origins of perivascular (or mural) cells, of which those adjacent to the vascular endothelium are termed pericytes for this purpose. These studies laid the groundwork for our understanding that pericytes derive from progenitor mesenchymal pools of multiple origins in the vertebrate embryo, some of which persist into adulthood. The results obtained through xenografting, like in the methodology described here, complement those obtained through genetic lineage-tracing techniques within a given species.

Meningeal Melanocytes in the Mouse: Distribution and Dependence on Mitf

Summary: Melanocytes are pigment producing cells derived from the neural crest. They are primarily found in the skin and hair follicles, but can also be found in other tissues including the eye, ear and heart. Here, we describe the distribution of pigmented cells in C57BL/6J mouse meninges, the membranes that envelope the brain. These cells contain melanosomes of all four stages of development and they depend on Microphthalmia associated transcription factor (MITF), the master regulator of melanocyte development, suggesting that they are bona-fide melanocytes. The location of these pigmented cells is consistent with the location of meningeal melanomas in humans and animal models.

Significance: Here, we document and define pigmented cells in the meninges of the mouse brain and confirm that they are melanocytes. This is important for understanding the role of this cell type and for understanding primary meningeal melanoma, a rare disease that likely arises from normal meningeal melanocytes.

Body pigmentation as a risk factor for the formation of intracranial aneurysms

Recent studies demonstrated pigmented cells both in the murine heart, in pulmonary veins, and in brain arteries. Moreover, a role for melanocytes in the downregulation of inflammatory processes was suggested. As there is increasing evidence that inflammation is contributing significantly to the pathogenesis of intracranial aneurysms, melanocyte-like cells may be relevant in preventing age-related impairment of vessels. As pigmentation of the heart reflects that of coat color, aspects of body pigmentation might be associated with the incidence of intracranial aneurysms. We performed a case-control study to evaluate associations between the pigmentation of hair and eyes and the formation of aneurysms. In addition to hair and eye color, constitutive and facultative skin pigmentation were assessed in a replication study as well as individual handedness which can be seen as a neurophysiological correlate of developmental pigmentation processes. Hair pigmentation was highly associated with intracranial aneurysms in both samples, whereas eye pigmentation was not. In the replication cohort, facultative but not constitutive skin pigmentation proved significant. The strongest association was observed for individual handedness. Results indicate a significant association of intracranial aneurysms with particular aspects of body pigmentation as well as handedness, and imply clinical usefulness for screening of aneurysms and possible interventions.

Primary sellar melanocytic tumor: report of new case and literature review

CONTEXT

Primary sellar melanocytic tumors are extremely rare, and they can mimic hormonally inactive pituitary macroadenoma both clinically and radiologically.

OBJECTIVES

The aim of this study was to describe a new case of primary sellar melanocytic tumor, and place it in the context of published literature.

DESIGN

This is a case report.

PATIENT

The case of a 61-year-old woman presenting with a 2-month history of fatigue and progressive bitemporal hemianopia is described. Endocrine investigation revealed anterior pituitary insufficiency and hyperprolactinemia without diabetes insipidus. Magnetic resonance imaging demonstrated a sellar tumor mass with suprasellar extension compressing the optic chiasm, and intense gadolinium enhancement. Transsphenoidal surgical excision of the pituitary tumor was undertaken. Histological examination showed a melanocytic tumor. An extensive search failed to find evidence of any other primary or secondary site. Due to the presence of significant tumor residue at 3-month follow-up, another surgical resection was done followed by post-operative stereotactic radiotherapy of the sellar region.

CONCLUSION

Primary sellar melanocytic tumors are exceptional lesions presenting most often as a tumor syndrome and/or anterior pituitary insufficiency mimicking a non-secreting pituitary macroadenoma. The management of these tumors consists of surgical removal of the tumor. However, surgery is often incomplete and stereotactic fractionated radiotherapy is frequently indicated.

Metastatic melanoma to the pituitary gland

BACKGROUND

Metastasis to the pituitary gland is unusual, and occurs most often in patients with carcinomas of the breast or lung. Despite its propensity for spread to the brain, metastatic melanoma has rarely been described within the sella.

METHODS

We report two cases of malignant melanoma pathologically confirmed within the pituitary, both metastatic from a primary site on the chest wall. In each patient, transsphenoidal resection of the tumor was incomplete and each received local radiotherapy after surgery.

RESULTS

One patient recurred quickly and developed brain metastasis as well. He died four months after resection of the pituitary metastasis, but the second patient survived six months without recurrence. As intrasellar metastasis portends widespread systemic disease and may be synchronous with parenchymal brain metastasis, survival in such patients is limited regardless of adjunctive therapy.

CONCLUSIONS

Such cases are likely to arise more commonly in future due to the increasing incidence of melanoma. Identifying them by imaging alone is difficult due to inconsistent signal characteristics on MRI (as shown by these cases) and the confusion introduced by any associated intratumoral hemorrhage.

Spatiotemporal gene control by the Cre-ERT2 system in melanocytes

The organ-specific and temporal control of gene activation/inactivation is a key issue in the understanding of protein function during normal and pathological development and during oncogenesis. We generated transgenic mice bearing a tamoxifen-dependent Cre recombinase (Tyr::Cre-ERT2) gene expressed under the control of a 6.1 kb murine tyrosinase promoter in order to facilitate targeted spatiotemporally controlled somatic recombination in melanoblasts/melanocytes. Cre-ERT2 production was detected in tissues containing melanocytes. After tamoxifen induction at various times during embryogenesis and adulthood in a Cre-responsive reporter mouse strain, genetic recombination was detected in the melanoblasts and melanocytes of the skin. Thus, the Tyr::Cre-ERT2 transgenic mice provides a valuable tool for following this cell lineage and for investigating gene function in melanocyte development and transformation.

Human melanocyte biology, toxicology, and pathology

The human melanocytes of the skin, hair, eyes, inner ears, and covering of the brain provide physiologic functions important in organ development and maintenance. Melanocytes develop from embryonic neural crest progenitors and share certain traits with other neural crest derivatives found in the adrenal medulla and peripheral nervous system. The distinctive metabolic feature of melanocytes is the synthesis of melanin pigments from tyrosine and cysteine precursors involving over 100 gene products. These complex biochemical mechanisms create inherent liabilities for melanocytic cells if intracellular systems necessary for compartmentalization, detoxification, or repair are compromised. Melanocyte disorders may involve pigmentation, sensory functions, autoimmunity, or malignancy. Environmental factors such as ultraviolet radiation and chemical exposures, combined with heritable traits, represent the principal hazards associated with melanocyte disorders.

A rare primary sellar melanoma. Case report

The authors report on the case of a 37-year-old woman in whom a primary sellar malignant melanoma mimicking a hemorrhagic pituitary macroadenoma was treated. This entity is exceedingly rare; only five cases are described in the literature. The patient presented with rapid deterioration of vision within a 2-week period. After an ophthalmological diagnosis of chiasmal syndrome was made, magnetic resonance (MR) imaging of the head revealed an intra- and suprasellar mass that was elevating and compressing the optic chiasm. Because of the signal heterogeneity of the lesion a hemorrhagic pituitary macroadenoma was assumed; the lesion was transsphenoidally resected. Histological examination of the specimen showed a malignant melanocytic tumor with immunopositivity for S100 protein and HMB-45. Despite extensive staging no other primary melanotic tumor was found. Thus, a primary sellar melanoma was diagnosed. Postoperative MR images demonstrated no residual tumor. For adjuvant therapy the region around the sella turcica received 40.4 Gy stereotactically guided radiation. A 24-month follow-up examination revealed no tumor recurrence. This represents the sixth case of such a lesion reported in the literature, the third case evaluated using MR imaging, and the first case with a progression-free survival of 24 months. Thus, the authors advocate that management of primary sellar melanoma should include gross-total removal and postoperative stereotactic radiotherapy.